Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuels.
Small-sized mobile devices use one or several battery cells for each device. On the other hand, middle- or large-sized devices, such as vehicles, use a middle- or large-sized battery module having a plurality of battery cells electrically connected to one another because high power and large capacity are necessary for the middle- or large-sized devices.
Preferably, the middle- or large-sized battery module is manufactured so as to have as small a size and weight as possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the middle- or large-sized battery module. Especially, much interest is currently focused on the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the weight of the pouch-shaped battery is small, the manufacturing costs of the pouch-shaped battery are low, and it is easy to modify the shape of the pouch-shaped battery.
Also, a battery module is a structural body including a plurality of battery cells which are combined with each other, with the result that the safety and the operating efficiency of the battery module may be lowered when overvoltage, overcurrent, and overheating occur in some of the battery cells. Consequently, a sensing unit for sensing the overvoltage, overcurrent, and overheating is needed. Specifically, a voltage sensor is connected to the battery cells so as to sense and control the operation of the battery cells in real time or at predetermined time intervals.
A secondary battery is being used as a power source for vehicles as a result of the extension of an application range of the secondary battery. For this reason, it is necessary to maintain a stably connected state of the sensing unit even when strong impact or vibration is applied to the secondary battery.
In a conventional battery module, therefore, voltages of the battery cells are sensed in a mechanical coupling manner using bolts and rivets or in a point contact manner using springs.
In the mechanical coupling manner using bolts, bus bars are coupled to electrode leads of the battery cells by bolts at a predetermined torque. In this coupling manner, the bolts may be loosened due to external force such as vibration. Consequently, reflection and management of an optimum torque value are necessary so as to prevent the bolts from being loosened. Also, stress is concentrated on electrode leads, which are relatively weak, and the electrode leads are fatigued, with the result that holes formed in electrode terminal connections such that the bolts are coupled through the holes may easily break.
In the mechanical coupling manner using rivets, on the other hand, electrode leads of the battery cells are connected to each other via the rivets. In this coupling manner, a loosening degree of the rivets due to external force is less than in the mechanical coupling manner using bolts. Even in this coupling manner, however, it is necessary to form holes in electrode terminal connections such that the rivets are inserted through the holes, with the result that breakage similar to the breakage occurring in the mechanical coupling manner using bolts may occur.
That is, the mechanical coupling manner has a problem in that, when external force, such as vibration, is applied to a battery module, a sensing defect occurs due to loosening of the bolts, and, when external force is applied to the battery module, stress is concentrated on holes formed in the electrode terminals of the battery cells such that the bolts or the rivets are inserted through the holes, with the result that breakage of the holes occurs.
In the point contact manner using springs, sensing is performed by direct point contact between the electrode leads of the battery cells and the springs. That is, sensing through the overall surface is not performed but voltage of a corresponding battery cell is sensed using a specific point. In this point contact manner, however, the sensing surface may be separated due to external force, or foreign matter may be introduced between sensing parts, with the result that it may not be possible to perforin stable voltage sensing.
Consequently, there is a high necessity for a voltage sensing member having a specific structure that is capable of performing stable sensing with respect to electrode leads of battery cells and a battery module including the same.